Lakesha James (center), daughter of Jill May, wipes a tear from her face as she answers a reporter's questions while standing with her husband Gary James (left) and brother Ricky James Jr. (right) outside of Department 24 at the Hall of Justice on Monday, September 30, 2013 in San Francisco, Calif.

Photo: Lea Suzuki, The Chronicle

Lakesha James (center), daughter of Jill May, wipes a tear from her...

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Defense Attorney Michael Gaines leaves Department 24 at the Hall of Justice on Monday, September 30, 2013 in San Francisco, Calif.

At 49, Jill May was many things - a homeless, drug-addicted prostitute, a street survivor trying to get her life together and a mother yearning to be close to her three children.

But in 2007 she took on one final role that led to her being doused with gasoline and burned alive in a desolate San Francisco parking lot near Candlestick Park, city prosecutors said Monday.

She was, in the mind of her alleged killer, "a snitch," Assistant District Attorney Michael Swart told a Superior Court jury on the first day of the trial in May's slaying, which prompted national outrage over its barbarism.

Swart said the defendant, 36-year-old Mia Sagote, had beat up May and left her naked in the Tenderloin the day before she lit her on fire - and after May told police what happened, she in effect sealed her own death warrant.

"This horrendous murder that you'll be hearing has its beginning in the seedy world of crack cocaine," Swart said in his opening statement. "And in this world there is one rule - you don't talk to police. You don't snitch."

Multiple charges

Sagote faces felony counts of murder, kidnapping, robbery and conspiracy to kidnap, along with four special circumstances including murder with torture. She would be eligible for the death penalty, but prosecutors are instead seeking a maximum of life in prison without parole.

The defendant, wearing a gray pant suit and a black ponytail, sat impassively throughout the opening statements of the prosecutor and her lawyer, Michael Gaines. Once, as Swart laid out the details of May's death, she dabbed her eyes with a finger.

May's daughter and one of her two sons sat 20 feet to Sagote's left, viewing for the first time the woman accused of killing their mother.

Lakesha James, 33, of Monterey County said she hadn't seen her mother for years before her death, but recalled that as May began shaking addictions to crack and heroin and finding housing in the mid-2000s, she had hopes of reuniting.

Years of haunting

Investigators say the beginning of May's grisly end came early in January 2007 when her longtime partner and father of her children, Ricky Smith, stiffed Sagote on $150 he owed her for crack. When Sagote came to collect on Jan. 11, she found only May - and, enraged, beat her and stripped her behind a dumpster, Swart said.

Talked with police

After a cop found May there, naked and dope-sick from a lack of heroin, she told the officer what happened to her.

Hearing that May had talked to the cops, Sagote came back the next day with cohort Leslie Siliga and kidnapped May, Swart said. Filling a gas can at a station on the way, they took her to a parking lot at Candlestick Point, he said.

"Jill May was there on her knees crying," Swart said. "Mia poured that gas can on Jill and went looking for a lighter... then lit a sock on fire and threw it on Jill May."

Gaines retorted that 37-year-old Siliga was actually the killer, but cut a plea deal in March to turn against Sagote. He told the jury that the witnesses against his client were either unreliable street characters or gave conflicting information.